Optimization Strategies for FeSiCr-Based Soft MagneticPowder Cores Structures and Magnetic Performance based on Interfacial Solid-Phase Reaction and Control of Powder Size Ratio

The preparation of insulating layers via interfacial solid-phase reactions is regarded as one of the most effective strategies for enhancing the magnetic performance of soft magnetic powder cores (SMPCs). However, mismatches in lattice structures between the insulating layer and the magnetic powder can cause cracking in the insulating lay-er, thereby compromising the stability and performance of SMPCs under operational conditions. This study presents a refined method for preparing insulating layers based on solid-phase reactions, utilizing the thermal decomposition of salt compounds in combination with powders of differing particle sizes: 99.4 μm (S1) and 8.9 μm (S2). In-itially, the FeSiCr(S1+S2)/ZnSO4 composite powder was synthesized through a hydro-thermal method. Subsequently, FeSiCr(S1+S2)-based SMPCs with a SiO2@Cr2O3@ZnO (SCZ) composite insulating layer were successfully prepared by a combination of heat treatment and cold pressing. This study then investigated the effect of varying powder ratios of different particle sizes on the microstructure and magnetic performances of FeSiCr(S1+S2)/SCZ SMPCs. Results revealed that ZnSO4 decomposes into solid-phase ZnO and gaseous SO2 and O2 during heat treatment. Among these, O2 triggers the sol-id-phase reaction, causing non-magnetic Si and Cr atoms from the soft magnetic pow-der to migrate to the surface, leading to the formation of a composite insulating layer composed of SiO2, Cr2O3, and ZnO. The smaller FeSiCr(S2) powder enhances plasticity, filling gaps within the SMPCs during the coating process and providing more sites for ZnSO4 decomposition and insulating layer formation. This process allows for the uni-form growth of an insulating layer on the surface of the magnetic powder, thereby re-ducing the lattice mismatch while simultaneously increasing the magnetic phase con-tent. By controlling the ratio of different magnetic powders, the magnetic performanc-es of SMPCs can be targeted and optimized. The optimal magnetic performance was achieved at a powder ratio of 60 wt%:40 wt% (S1:S2), with maximum saturation mag-netization (172.9 emu/g), magnetic permeability (31.3 at 10 mT, 500 kHz), and low core loss (465.62 kW/m3 at 30 mT, 200 kHz). These findings suggest that the optimized SMPCs are promising candidates for high-performance electromagnetic components.